This invention relates to connecting hitches for coupling a truck tractor to a trailer, and more particularly to a fifth wheel hitch support structure.
A fifth wheel hitch support that shifts laterally in an arc to stabilize a trailer during side tilt of the trailer is set forth in U.S. Pat. No. 3,122,382. The stability resulting from this structure has caused it to gain considerable acceptance. A subsequent version of the apparatus is also set forth in Australian Pat. No. 436,212 dated July 18, 1968, and New Zealand Pat. No. 153,126 dated July 15, 1968.
The function of these hitches is such that a movable frame can arcuately laterally shift on a stationary frame in response to trailer tilt or uneven terrain, to keep the trailer center of gravity directly over the tractor frame for stability. This movement is limited in either direction by stops, typically using rubber snubbers which provide some shock absorber effect at the very limits of movement. When the trailer moves beyond the uneven terrain, gravity forces operating through the trailer returns the fifth wheel plate.
Using such a hitch, it has been found that, as the trailer tilts varying amounts during this stabilizing action, the driver may actually be unaware of the tilting action or the extent thereof until the movable frame strikes the stop at the extreme shifted position. Ideally, the driver should be constantly aware when this stabilizing movement is occurring, and the extent to which it is occurring since, the more knowledge the driver has to the actions of his rig, the more confidence he has in his control of it. Specifically, ideally the driver should be provided with the facility to "feel" or "sense" the trailer tilt stabilizing movement, and the extent of movement occurring. This factor stimulated the efforts toward conceiving this present development.
Actually, the present development not only provided a benefit relating to this factor, but also provided a solution to another seemingly unrelated problem experienced during uncoupling and recoupling with this type of fifth wheel hitch. Specifically, when a tractor is detached from a trailer that is on uneven terrain, the fifth wheel can be in a laterally tilted condition such that, when the driver attempts to recouple the tilted fifth wheel to another trailer on different terrain, difficulty can be experienced because of the fifth wheel being cocked relative to the orientation of the kingpin on the second trailer. This can cause damage to the equipment or at least, extra effort by the driver to straighten up the fifth wheel plate.